Nickel-chromium-cobalt alloys for use at relatively high temperatures

ABSTRACT

NICKEL-CHROMIUM-COBALT-BASE ALLOYS CONTAINING CORRELATED AMOUNTS OF TITANIUM, ALUMIUM, COLUMBIUM AND, WHEN PRESENT, MOLYBDENUM, AS WELL AS CARBON AND OTHER CONTITUENTS OFFER A COMBINATION OF HIGH TEMPERATURE STRESS-RUPTURE STRENGTH, DUCTILITY AND IMPACT RESISTANCE   TOGETHER WITH GOOD CORROSION RESISTANCE OF SUCH MAGNITUDE AS TO RENDER THE MATERIALS SUITABLE FOR VARIOUS GAS TURBINE ENGINE COMPONENTS.

March 27, 1973 E. G. RICHARDS ET AL NICKEL-CHROMIUM-COBALT ALLOYS FOR USE AT RELATIVELY HIGH TEMPERATURES Filed March 4, 1970 4 Sheets-Sheet 1 Ti til.

INVENTORS Z- bA A D @emyfzqws 3y Q05 ASM/QVfW YE Mom/54 dam F 0m WJI. ML

"March 2 7, 1973' firms/w- 72 7 Psewvr A Filed March 4, 1970 E. G. RICHARDS ETAL NICKEL-CHROMIUM-COBALT ALLOYS FOR USE AT RELATIVELY HIGH TEMPERATURES 4 Sheets-Sheet 2 dis Pavcavr C15 INVEN7UR5 Wm. PM

' US. Cl. 75-171 United States Patent 3,723,107 NICKEL-CHROMIUM-COBALT ALLOYS FOR USE AT RELATIVELY HIGH TEMPERATURES Edward Gordon Richards, West Hagley, Paul Isidore Fontaine, Solihull, and Michael John Fleetwood, Berkhamsted, England, assignors to The International Nickel Company, Inc., New York, N.Y.

Filed Mar. 4, 1970, Ser. No. 16,091 Claims priority, application Great Britain, Mar. 7, 1969, 12,261/ 69 Int. Cl. C22c 19/00 2 Claims ABSTRACT OF THE DISCLOSURE Nickel-chromium-cobalt-base alloys containing correlated amounts of titanium, aluminum, columbium and, when present, molybdenum, as well as carbon and other constituents offer a combination of high temperature stress-rupture strength, ductility and impact resistance together with good corrosion resistance of such magnitude as to render the materials suitable for various gas turbine engine components.

As those skilled in the art are aware, research eiforts have been endless in the quest of alloys capable of delivering in use certain metallurgical properties. Usually such alloys have been of the nickel-chromium or cobaltchromium-base variety (rather exotically termed superalloys) and have found extensive utility in a number of high temperature applications. Commonly these alloys contain one or more such elements as titanium, aluminum, columbium (niobium), molybdenum, etc., primarily for the purpose of imparting strength and hardness properties.

However, such characteristics as strength and hardness, including elevated temperature stress-rupture strength, are by no means all encompassing in respect of the properties such alloys might be called upon to exhibit. Resistance to high temperature corrosion, for example, is often an indispensible necessity, depending, of

course, upon the intended application. And this aspect plus other considerations, e.g., tensile ductility, the ability to absorb impact energy upon prolonged exposure, etc.,

focus attention on the objectives of the subject invention since such properties usually do not go hand in hand.

It has been demonstrated, for example, that with increasing chromium content the ability of various nickelchromium-cobalt-base alloys to resist corrosion at high temperatures, in, say, sulfur-containing environments is significantly improved. But it has also been shown that increasing the chromium level is not without its drawbacks. For example, in such alloys high percentages of chromium have been known to induce loss in stressrupture life. Another adverse elfect can be a decrease in the amount of the hardening and strengthening elements titanium, aluminum, columbium and molybdenum that may be present without causing alloy embrittlement upon prolonged exposure to high temperatures. Accordingly, the present invention is directed in the main to minimizing these conflicting effects.

In any case, it has now been discovered that an excellent combination of high temperature stress-rupture strength, ductility and impact strength can be attained together with good corrosion resistance, illustratively in respect of hydrocarbon fuels containing sulfur or in marine environments in which chlorides might be injected into, say, gas turbine engines, with high chromium, nickel-base alloys containing special amounts of titanium, aluminum, columbium, and other elements as described herein, including, under certain compositional limitations, molybdenum.

3,723,107 Patented Mar. 27, 1973 Generally speaking and in accordance with the present invention, alloys contemplated herein contain (in weight percent) from 19.5% to 23% chromium, about 0.01% to 0.2% carbon, about 10% to 24% cobalt, from 3% to 7% in total of titanium plus aluminum, the ratio of titanium to aluminum being from about 1:1 to 4: 1, from about 0.5% to 2% columbium, with the proviso that the total percentage of titanium plus aluminum is so related to the percentage of columbium that it is represented by a point in the area ABCDEA of the accompanying drawing, up to 4.5% molybdenum, from 0.001% to 0.05% boron, e.g. 0.01% to 0.01% or 0.02%, up to 0.15% zirconium, with the further proviso that ten times the percentage of boron plus the percentage of zirconium is at least 0.02%, upto about 0.1% hafnium, up to about 0.04% magnesium, up to about 0.3% rare earth metal, up to about 2% yttrium, and the balance, apart from impurities, being essentially nickel.

In carrying the invention into practice, the minimum chromium content of 19.5% is dictated by the need for the greatest corrosion-resistance, but more than 23%, having in mind the relatively high total percentage of titanium, aluminum, columbium and molybdenum that can be employed, leads to embrittlement or loss of stressrupture strength or both. 'In striving for the best combination of results the chromium should be from 20.5% to 22.5%.

If the percentage of carbon is below 0.01%, stressrupture strength is reduced. On the other hand, too much carbon renders the alloys susceptible to embrittlement, and it should therefore not exceed 0.2%. A range of 0.015% to 0.08% is most beneficial.

Cobalt strengthens the alloys and at least 10%, preferably at least 14%, is required for this purpose. Should the cobalt exceed 24% the alloys tend to .undesirably embrittle on prolonged heating and advantageously it does not exceed 22%.

The alloys are further and principally strengthened by titanium, aluminum, columbium and, provided certain conditions are observed, the presence of molybdenum is also most advantageous. Within the composition ranges set forth herein, the percentages of columbium and molybdenum and the sum of the contents of titanium and aluminum must also be interrelated in a manner that will be described with reference to FIG. 1 of the accompanying drawing. Prefacing this however, it should be emphasized that stress-rupture life is generally improved by colurnbium, and the alloys must contain at least 0.5% and preferably at least 1.0% thereof. Should the columbium exceed 3% the alloys have inadequate stress-rupture lives and may tend to embrittle. Moreover, subject to what is set forth hereinafter, as the molybdenum content increases stress-rupture life increases, and it is most beneficial that the alloys contain at least about 2% molybdenum.

Turning to FIG. 1, when the alloys are molybdenumfree, the (Ti+Al) and Ch contents must be represented by a point in the area ABCDEA, where the point C is 6% (Ti+Al) and 3% Ch. When the alloys contain 2% molybdenum, the amounts of (Ti+Al) and Cb must be represented by a point in the area A B C D EA where the point C is 5.65% (Ti+Al) and 2.7% Cb, and when the alloys contain 4% molybdenum, the (Ti+Al) and Cb percentages must be represented by a point in the area A B C D4EA where the point C, is 4.6% (T i+Al) and 1.8% Cb. Corresponding areas defining the relationship between (Ti+Al) and Cb for other contents of molybdenum between 0 and 4.5% are obtained by the following geometrical construction. A line is drawn from the point X (7.9% Ti-l-Al and 3.4% Cb) through the point of the line AF corresponding to the molybdenum content (n percent) of the alloy, and extended to interwere generally inferior in respect of one or other propsect the line AB in the point A which represents the erty to the alloys according to the invention having commaximum (Ti-t-Al) content of the alloy. The point B positions within the area. Within the areas, the stressis given by this (Ti-l-Al) content and Cb=1%. The rupture life increases with the (Ti-l-Al) content. It is point C is the intercept of the line CC, and a line through to be pointed out in this regard that if the percentage B parallel to the line BC, and the point D is the point of molybdenum does not exceed 2% it is of considerable on the line DE (Ti+Al=3.7%) at the same Cb content benefit if the total amount of Ti-l-Al is at least 4.5%.

as C In this way the area A B C D EA is obtained for It should also be mentioned in terms of the respective molybdenum contents of 3%. amounts of titanium and aluminum, that at ratios of For a given molybdenum content, if the (Ti-l-Al) titanium to aluminum less than 1:1, stress-rupture ductiland Cb contents corespond to a point above or to the ity and impact strength are reduced, while if the ratio right of the area defined in this way, one or generally exceeds 4:1 the stress-rupture strength is inadequate. In both of the impact Strength and Stress-rupture ductility consistently achieving good results the ratio should be (elongation) of the alloy is impaired. from 1:1 to 2.5 :1.

The efiects imparted y titanium, aluminum, Colllm- The resistance of alloys according to the invention to bium and molybdenum, are illustrated by the results of corrosion b h combustion products of impure h d tfests 011 a of alloys having the aI1a1YZd p carbon fuels and by marine salts has been determined Hons Set forth Table L and nomlnany also 9 by tests in which specimens of the alloys were exposed boron and ).05% zirconium, the balance being nickel to a molten mixture of 25% by Weight of sodium ch1o and impuritles. After vacuum-melting an addition of ride and 75% sodium sulfata at c The corrosion 2 magpesmm was .made as a N1'15% Mg alloy damage was assessed by comparing the weight of each glVlIlg a residual magnesium content of 0.02%, and the B after removin the corrosion roducts b alloys were vacuum-cast. The ingots were hot-worked to Spam h d h y bar from which stress-rupture test-pieces were machined F f f ,iescalmg m mo ten so mm y mm 1 wlt the and given a heat treatment consisting of solution heating 9 Welght before exposure The resistant for 4 hours at 11500 C air cooling, aging for 16 hours terials are those that show the least loss in weight. at 850 C., and again air cooling. The stress-rupture The tests were Performed in two Ways: life and elongation to rupture were determined on speci- Test A: Samples of each alloy were half-immersed in mens of each alloy under a stress of 17 ton-f./1n. at the Salt mixture While heated in air.

Test B: Samples of each alloy were heated in a vertical 815 C. Further test-pieces were solution heated for 4 0 hours at 1150 C., air cooled, and then heated for 1000 hours at 850 C., and again air cooled, the Charpy V-notch impact strength being thereafter determined at open-top furnace into which the salt mixture was con tinuously fed as a fine dispersion at a rate of 5 g./hour.

room temperature. The results are set forth in the last The results obtained for Alloy 14 are set forth in Table three columns of Table I. Alloys identified by a numeral are within the invention, the others being outside the scope thereof.

ive of alloys in 35 II, the results being generally representat accordance herewith.

TABLE I Stress-rupture Impact Liio Elong strength Mo (hr-s.) (percent) (IL-lbs.)

Composition (percent by weight) 'Ii Ti+Al Alloy No.

5550000009500050 a taatia tat a 22 2 2233 am 3 9 00 9 00 1 221 12 727575515517055524229-2222 229 G .6 .0 .2 .2 .4 .22222 222 110 .0 .21 .0 0 1 .922 101 1 222%2m22m2 2 2%122 222 2 54455555 51 0 5 4 3627nma m mmewwmmjnwnmj wjfio 4 t4 .5 5 3 4a 4 6 4 344 5 5 57555 50035 5555 52 5 490 893 m5 7 11 ILL 1 .1 1 1111111 TABLE III Alloy No. 14

Points corresponding to the composition of each alloy in Table I are plotted on FIGS. 2 to 4 of the accompanying drawing, which represent the areas from FIG. 1

Composition: Wt. percent 1 0.036

corresponding to molybdenum contents of 0%, 2% and 4%, respectively. The first figure in parentheses for each alloy is the stress-rupture life in hours, the second figure the elongation in percent, and the third figure the impact 3 1 strength. It will readily be seen that the alloys, whose 1,55 composition fell outside the areas 1.05

Balance nickel, impurities and nominally 0.05% Zr and TABLE IIIContinued Weight loss (mg./cm.

As to other alloying constituents, boron and to a lesser extent zirconium, both improve the stress-rupture strength, and the alloys must contain at least 0.001% but not more than 0.05% boron, since amounts larger than 0.05% boron impair the forgeability of the alloys. Zirconium may be present in amounts up to 0.15%, and the combined amount of boron and zirconium, as expressgd by percent B+percent Zr should be at least 0.02 o.

Hafnium can be present in amounts up to 0.1%, for example, from 0.02% to 0.07%, to improve weldability, especially those containing both boron and zirconium. Magnesium is advantageously added in amounts up to 0.04% to improve workability, but larger amounts have the opposite effect and make working more difiicult. Most suitably the magnesium content is from 0.01% to 0.03%.

The resistance of the alloys to oxidation and scaling is improved by the presence of rare earth metals, and one or more of these metals may be added, for example, in the form of Mischmetall. Advantageously from 0.01% to 0.3% of rare earth metal, e.g., from 0.03% to 0.08%, is added.

We find the yttrium additions also improve the oxidation and scaling resistance of the alloys and their resistance to sulfidation, and yttrium can advantageously be added in amounts from 0.2% to 2%, for example, from 0.5% to 10%. As an example of an yttrium-containing alloy, Alloy No. 18, which contains 0.04% C, 22% Cr, Co, 4% Mo, 3.1% Ti, 1.6% A1, 1% Cb, 0.05% Zr, 0.003% B and 1% Y, the balance, apart from impurities, being nickel, had after heat treating as for the alloys in Table I, a stress-rupture life at 17 ton-f./in. at 815 C. of 403 hours with an elongation of 8.6% and a Charpy V- notch impact strength at room temperature, after heating at 850 C. for 1000 hours, of 12.2 ft. lb.

Of the elements that may be present as impurities, silicon has a deleterious effect on corrosion-resistance and should therefore be kept below 1% and preferably below 0.5%. Other impurities may include manganese in amounts up to 1% and iron in amounts up to 2%. Tantalum may be introduced incidentally with the columbium in an amount up to about one-tenth of the columbium content. For the purposes of the present invention, such amounts of tantalum are to be regarded as part of the columbium content.

A particularly advantageous combination of properties is exhibited by alloys containing from 20.5% to 22.5% chromium, 15% to 22% cobalt, from 0.015%, e.g., from 0.03% or 0.035%, to 0.08% carbon, 4% to 5% titanium plus aluminum with a Ti:Al ratio of from 1:1 to 2.5:1 or 3:1, 1.0% to 1.7% columbium, 3.5% to 4.2% molybdenum, 0.001% to 0.006% boron, 0.03% to 0.06% zirconium, up to 0.03% magnesium, up to 0.07% hafnium, up to 0.3% rare earth metal and up to 1% yttrium, the balance, apart from impurities, being nickel.

To develop the full stress-rupture properties of the alloys in wrought form they must be subjected to a heat treatment comprising solution heating and subsequent aging. The solution treatment may consist of heating from 1 to 8 hours in the temperature range of 1050" C. to 1250 C., and the alloys may then be aged by heating for 1 to 24 hours in the temperature range of 600 C. to 950 C. An intermediate aging treatment consisting of heating for 1 to 16 hours at 800 C. to 1050 C., may be interposed between the solution treatment and the final aging stages. The alloys may be cooled at any convenient rate after each heat treatment stage, e.g., by air cooling 6 (generally to room temperature) or by direct transfer from a furnace at one temperature to one at a lower temperature.

The alloys can be air-melted, but to ensure the best creep properties they are preferably melted and cast under vacuum. They can be readily processed by conventional means such as extrusion, forging, or rolling. Although they are primarily intended for use in the wrought form as gas turbine blades they are suitable for use in other applications where a combination of good stressrupture strength and resistance to corrosion is required, particularly for articles and parts that are subject in use to stress at high temperatures while exposed to the combustion products of impure hydrocarbon fuels or to salt or both. They may also be used to make cast articles and parts, which may also require heat treatments to develop their strength properties.

The alloys of the invention are also useful as matrix materials for alloys dispersion-hardened by the presence of finely divided refractory particles such as thoria, yttria, lanthana, ceria, or rare earth oxide mixtures, such as didimia. The refractory compound may suitably be present in an amount of at least 0.2%, preferably 0.5 to 5%, by volume and the particles should preferably be maintained as fine as possible, for example below 0.5 micron, most suitably from 10 angstroms to 1000 angstroms (0.001 to 0.1 micron). The present invention includes the use of the alloys as matrix materials in dispersion-hardened alloys.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. A nickel-chromium alloy characterized by a combination of good stress-rupture strength, tensile ductility and the ability to absorb impact energy together with good resistance to various corrosive media, the stress rupture strength being at least about 300 hours at a temperature of about 815 C. under a stress of 17 ton-f./in. said alloy consisting of from 19.5% to 23% chromium, about 0.01% to about 0.2% carbon, from 10% to 24% cobalt, about 3.7% to 7% in total of titanium plus aluminum, the ratio of titanium to aluminum being from 1:1 to 4:1, from 0.5% to 3% columbium, up to 4.5% molybdenum, with the proviso that the total percentage of titanium plus aluminum is correlated with the columbium and molybdenum so as to represent a point within the area ABCDEA of FIG. 1 of the accompanying drawing, from 0.001% to 0.05% boron, up to 0.15% zirconium, the sum of 10X percent B+percent Zr being at least 0.02%, up to 2% iron, up to 1% silicon, up to 1% manganese, and the balance essentially nickel.

2. An alloy in accordance with claim 1 containing from 20.5% to 22.5 chromium, from 0.015% to 0.08% carbon, 15% to 22% cobalt, 4% to 5% titanium plus aluminum, the ratio of titanium to aluminum being up to 3:1, 1.0% to 1.7% columbium, 3.5% to 4.2% molybdenum, 0.001% to 0.006% boron, 0.03% to 0.06% zirconium, up to 0.03% magnesium, up to 0.07% hafnium, up to 0.3% rare earth metal, and up to 1% yttrium.

References Cited UNITED STATES PATENTS 2,570,193 10/1951 Bieber et al. 75l7l 3,479,157 11/1969 Richards et a1 75-171 3,516,826 6/1970 Ward et al. 75l71 RICHARD 0. DEAN, Primary Examiner mg Q v UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 723,107 Dated March 27, 1973 InventoflaEdWard Gordon Richards, Paul Isidore Fontaine 81 Michael John Fleetwooc in the abovddentified patent It is certifid that error appears acted as shown below:

and that said Letters Patent are hcreby cor:

Coiumn 2, line 12, for "0. 01%"fiT'st occurrence, 'read "0.001%";

Table I, Alloy-N0 K, column "Ti", for "23 read "2.3";

Column 5, line 43, for "12.2" read "15.2";

Signed sealed this 22nd day of January 1970..

(SEAL) AtteSt:

EDWAR M FLET HEB R. RENE D. 'I'EGTMEYER Attostlng offlcer Acting Commissioner of Patents 

